Ionic control of porin permeability in bacteria.

Gram-negative bacteria are sneaky little things. They don’t like to be killed so they have this medieval double-wall protecting them from the outside. They, however, still need to import food and nutrients. Therefore, this external wall is plaged with pore-like proteins called - guess what - Porins! It is believed that these channels are always open to allow the traffick in and out of the outer membrane. But if that is the case… how can bacteria build a membrane potential? The membrane potential is the accumulation of protons across the inner membrane that the bacteria uses to produce ATP and a myriad of other biological processes. That is, if the protons are accumulated in the periplasm and the porins and open, why they don’t leak out? That is what I call the membrane potential paradox. So, how do bacteria control this balancing act?

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